Various wireless technologies for both near-field and far-field charging now exist. These include inductive, resonant, RF, ultrasound, and infrared charging. They are governed by different standards with their associated trade-offs. As consumers warm up to a world without cables, wireless charging technology is positioned to explode.
What is wireless charging? What differentiates one technology from another? Let us start with answering these questions.
A lot of people reduce wireless charging to inductive or short-distance resonant charging. While both are forms of wireless charging, they do not represent all possible scenarios. The word “wireless” indicates the elimination of cables and adapters; what consumers really want is both freedom from cables and freedom from trouble. They want an unlimited power source for their devices.
The near-field methods with inductive and resonant charging can’t satisfy the consumer’s appetite. Both inductive and resonant charging simply replace the “plug in” with the “place on” user experience. There is excitement in emerging technologies that encompass RF, ultrasound, WiFi, and Infrared.
The ideas sound great and the vision of a world that is never out of power is achievable, but the path is paved with demands for collaboration between multiple entities, creating a supply chain pyramid.
- Device manufacturers are the top of the supply pyramid because we use these devices daily and they create the front line of user experience. These include brands for cell phones, sports watches/fitness bands, smart home appliances, and automobiles. The UK has reportedly initiated an effort to build “Electric Recharging Lanes” to reduce the chance of electrical vehicles running out of power. Intel has promised to provide a cable-less laptop in 2017. Google and others are working on cable-less charging systems for fleets of electric vehicles. Each device manufacturer has their own power transmitter and receiver, such as charging mats and stands. The device manufacturers decide which charging method to use in order to optimize user experience and maximize revenue return.
- The middle of the pyramid includes standards agencies, technology enablers, and systems manufacturers. This middle layer is hidden from the consumer, but is critical for end success and technology adoption. This layer runs the first risk of obsolescence as new technologies and methodologies emerge.
Various charging standards have been created in the past decade in an attempt to regulate near-field charging. The Qi standard is driven by the Wireless Power Consortium (WPC) (Inductive: single device at short distance); established in 2008, and currently boasts over 200 member companies. It transfers about 5W, which is sufficient for smartphones. Rezence driven by A4WP (Resonance charging with distance: multiple devices over longer range). PMA is very similar to Qi with the difference in operation frequency.
Charging standards define the compatibility between devices, meaning that a charging mat designed with Qi standard cannot charge a phone designed with the PMA specification. Each standard defines the type of coil coupling, configuration, and the communications protocol to be used for wireless devices. In order to adapt to the different devices powered by various charging standards, infrastructure companies have to support both.
In June 2015, the Alliance for Wireless Power (A4WP) and the Power Matters Alliance (PMA) announced a strategic merger that shook up the wireless charging industry. In November 2015, the new organization rebranded itself as the AirFuel Alliance. The merger is a step forward to fulfill the vision that wherever a consumer goes, whether it is in restaurants, cars or at home, device charging will be interoperable and convenient.
Far-field charging has been explored with RF, ultrasound and infrared. No matter what technology it is based on, the concepts are all similar, but use specific transducer technology: The RF uses antenna-to-antenna, the light transmits to a transducer to convert the photons to electrical energy, and the ultrasound converts the pressure of ultrasonic waves into energy. Each technology has limitations; ultrasound and light can’t travel through walls and RF power falls off considerably with distance.
All of these technologies aim at beaming focused power to coupled devices at specific locations instead of broadcasting evenly in space. This directed beaming can relieve health concerns and improve transfer efficiency. Just as with near-field charging, the receiver enabled with one technology cannot be charged with the power transmitter that beams power through a different medium. An RF-based fitness watch cannot communicate with an ultrasound based power transmitter.
These charging standards define the languages each device speaks. While it is great to have competition among the standard organizations specific applications need to emerge to create guaranteed interoperability.
Technology enablers are the companies who design and manufacture ICs and transducers and supply them to the device manufactures. Semiconductor companies like Maxim Integrated offer a wide range of power products and solutions specifically for near-field wireless charging. It is critical for these companies to both innovate and follow the trend set by the charging standards, but they often have the capability to lead the market as well. As examples, both Energous and Ossia are trying to lead the trend in far-field charging enabled by the RF power ICs.
System manufacturers design accessories for existing consumer products and then empower them to enter the domain of wireless charging. Powermat is a great example of an intermediate technology for a phone not enabled for wireless charging. They manufacture a simple ring to engage with the charging mat and charge the phone. uBeam has been aiming at delivering a cell phone case to enable charging through ultrasound. Instead of embedding the wireless charging technology into consumer devices, these two companies focus on creating accessories to enable existing products with the complete solution.
The success of system manufactures, however, is highly dependent on the infrastructure. If the desks in the office already have charging mats embedded, or the conference room has an ultrasound power router installed, consumers are more likely to adopt compatible accessories.
- Safety and infrastructure are the bottom of the adoption pyramid. These are the most understated elements in the acceleration of wireless charging adoption. According to research conducted by IHS in 2014, 70% of consumers charge at least one device once a day. Home, office, and cars are the most common places for people to charge their devices. The deployment of wireless charging is a two-way street: Not only should devices support wireless charging technology, there should be plenty of hotspots for them to be charged. The adoption will come to full fruition once a base infrastructure is in place.
Safety is a concern for wireless charging, especially for the far-field power beaming. Radio frequency (RF) safety is determined by how much exposure can be applied without being harmful to human health. The Federal Communications Commission (FCC) regulates the safety level for human exposure to an RF field. The safety level is defined based on the combination of signal frequency and the energy it carries. Each RF-based technology aims at beaming small energy packets, and then having the receiving end accumulate and convert these packets to a usable energy level. The Specific Absorption Rate (SAR) is used to define these limits. It has been found that at certain frequencies and power levels, the increase of the skin temperature of a person is higher than other frequencies with similar power levels. The SAR defines frequency range and the amount of power that can be used near people so that the temperature rise is minimal. ANSI identified SAE J2954 on wireless charging design and UL 2750 on wireless charging safety as necessary. J2954 is essential to insure interoperability between the transmitter and the receiver when they are manufactured by different suppliers. Underwriters Laboratories (UL) has also been developing requirements for low-energy near-field power transfer. UL 2738 applies to inductive near-field power transfer system. UL has also been working on safety requirements for the wireless charging system for electrical cars. These regulations enforce the safe operation of end products before they are put on shelves for consumer adoption.
IKEA is the first major company to announce the rollout of wireless charging into home and office infrastructure, and automobiles have started to include wireless charging consoles as well. Should the device and system manufacturer partner with office utilities so that we have charging mats at each desk and/or routers in every conference room?
The consumer adoption of any innovative technology takes time. Wireless charging companies need to proactively seek partnerships with established infrastructure builders to speed up the process. Since homes are getting smarter, perhaps it is worth embedding wireless power transmitter technology within intelligent fire alarms, which are already being placed on ceilings. With the explosion of mobile and IoT devices, the adoption of in-vehicle, near-field, wireless chargers is expected to accelerate as companies like GM, Toyota, and Fiat/Chrysler all begin to include wireless charging for smartphones.
Wireless charging is not just about cutting the cord, power management, and convenience. It is more than inductive or resonant charging. The far-field charging is where the innovation can take place. Our electronic devices need to be smart enough to charge themselves. A dominant player, however, possesses the opportunity to accelerate adoption by establishing their own charging technology. At this early stage in the commercialization of wireless charging infrastructure companies run the rink of early obsolescence. Wireless charging OEM companies need to proactively reach out to established infrastructure builders to use the existing standards in order to speed up consumer adoption.
The adoption of wireless charging technology resides in multi-layered ecosystem building. The ultimate consumer adoption of each method requires seamless coupling between multiple entities: semiconductor, consumer device, furniture, retail, automotive, and public facilities.
The wireless charging technology that can gain the most momentum in this ever-changing eco system will survive and eventually thrive.
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